1. Field of the Invention
The present invention relates to a thermal protector used in various electric components and appliances for the purpose of protecting them from burning due to overheating and over-current accidents.
2. Description of the Prior Art
This kind of conventional thermal protector has been so constructed that an electrode mount with a movable electrode and a stationary electrode facing each other fixed thereon by a glass bead is encased in a glass envelope, the opening of the glass envelope located under the glass bead is melted by heating to conduct pinch-sealing thereof, and then the glass envelope is exhausted and filled with an inactive gas, after which the top of the glass envelope undergoes tip-off to complete a hermetic sealing (Japanese Utility Model Publication No. 56-42912, FIG. 2(a)).
Such a thermal protector is attached to the temperature risen location of various electric components and appliances and has a protective function as follows; when overheating or over-current occurs at the location due to something unusual, the snap-acting and thermo-sensitive element of a movable electrode reverses to separate from a stationary electrode, which interrupts the flow of electric current to the electric components and appliances.
With this kind of thermal protector, there has arisen a demand for the development of a thermal protector having a more miniaturized structure because of the trend toward miniaturization in various electric components and appliances. However, it has been difficult to miniaturize a conventional thermal protector in terms of its structure, because in a conventional structure, the shapes and the dimensions of a glass bead or a pinch-sealed portion, the distances between a glass bead and the internal surface of a glass envelope or between a glass bead and the internal surface of a pinch-sealed portion, etc., have been limited due to problems associated with hermetic sealing and glass crack.